//
// Created by spiro on 19-3-9.
//

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFSIZE 4096
#define SLEN 81
void append(FILE *source, FILE *dest);

char * s_gets(char * st, int n);

int main(void) {
    FILE *fa, *fs;
    int files = 0;
    char file_app[SLEN];
    char file_src[SLEN];
    int ch;

    puts("Enter name of destination file:");
    s_gets(file_app, SLEN);

    if ((fa = fopen(file_app, "a+")) == NULL) {
        fprintf(stderr, "Can't open %s\n", file_app);
        exit(EXIT_FAILURE);
    }

    if (setvbuf(fa, NULL, _IOFBF, BUFSIZE) != 0) {
        fputs("Can't create output buffer\n", stderr);
        exit(EXIT_FAILURE);
    }

    puts("Enter name of first source file (empty line to quit):");
    while (s_gets(file_src, SLEN) && file_src[0] != '\0') {
        if (strcmp(file_src, file_app) == 0) {
            fputs("Can't append file to itself\n", stderr);
        } else if ((fs = fopen(file_src, "r")) == NULL) {
            fprintf(stderr, "Can't open %s\n", file_src);
        } else {
            if (setvbuf(fs, NULL, _IOFBF, BUFSIZE) != 0) {
                fputs("Can't create input buffer\n", stderr);
                continue;
            }
            append(fs, fa);
            if (ferror(fs) != 0) {
                fprintf(stderr, "Err in reading file %s.\n", file_src);
            }
            if (ferror(fa) != 0) {
                fprintf(stderr, "Err in writing file %s.\n", file_app);
            }
            fclose(fs);
            files++;
            printf("File %s appended.\n", file_src);
        }
        puts("Next file (empty line to quit):");
    }

    printf("Done appending. %d files appended.\n", files);
    rewind(fa);
    printf("%s contents:\n", file_app);
    while ((ch = getc(fa)) != EOF) {
        putc(ch, stdout);
    }
    puts("Done displaying.");

    fclose(fa);
    return 0;
}

void append(FILE * source, FILE * dest) {
    size_t bytes;
    static char temp[BUFSIZE];

    while ((bytes = fread(temp, sizeof(char), BUFSIZE, source)) > 0) {
        fwrite(temp, sizeof(char), bytes, dest);
    }
}

char * s_gets(char * st, int n) {
    char * ret_val;
    char * find;

    ret_val = fgets(st, n, stdin);
    if (ret_val) {
        find = strchr(st, '\n');
        if (find) {
            *find = '\0';
        } else {
            while (getchar() != '\n') {
            }
        }
    }

    return ret_val;
}